Correct me if I'm wrong, but you said "jewels", so I'm assuming you have a pair, and I think a 29 gal is minimum for a pair of jewels, so you might not want to add anymore fish. Even if you could I don't think there is any kind of fish that will stay small enough live in a 29 and not get killed by the jewels.
Like I said, correct me if I'm wrong anybody, but this seems to be what I've found from research, I've been looking into getting a jewel.